1. Field of the Invention
The present invention relates to a data transfer device.
2. Description of the Prior Art
It is known to transfer data from a data source to a data utilization device via a buffer where for instance the instantaneous rate of data production of the source is greater than the rate of use of the data by the utilization device, but the average rate of production is equal to or less than the rate of use. It is also known to use a buffer where variations in the rate of production occur and it is desired to feed data to the utilization device at a constant rate; time base correctors for example carry out such a function.
It is known to connect computers and computer peripherals via an interface. A well known interface is an SCSI-2 interface conforming to the standard ANSI X 3.131-1994 which is described in, for example, the book "The SCSI bus and IDE Interface" by Friedholm Schmidt published by Addison-Wesley, ISBN 0-201-42284-0. The SCSI standard defines the physical characteristic of the interface and a complete set of protocol and commands. A SCSI interface can support a data transfer rate sufficiently high to transfer frames of digital video data at video frame rates, e.g. up to 40M bytes/second for a 32 bit SCSI bus. SCSI however, has a complex bus protocol and a complex set of commands.
It has been found that although data can be transferred via a SCSI interface at sufficiently high rate once transfer begins, the timing of the transfer cannot be accurately set because of the need to implement the complex bus protocol and because of variations in timing caused by SCSI controllers which implement the protocol and commands.
Other simple standard interfaces such as RS232 (described in the book mentioned above) and RS422 are also well known. The standards for such interfaces define the physical characteristics of the interfaces. A set of protocols may be defined for a particular application of the standard.